A heretofore known gas encapsulating structure (hereafter called a capsule structure) of an electromagnetic contactor is the kind of structure shown in FIG. 5 wherein, specifically, a fixed contact 26, a movable terminal 27 having a movable contact 27a, a movable shaft 28, a contact spring 29, and the like, are incorporated inside an arc extinguishing chamber 1. Also, a movable iron core 30 and return spring 31 to which the movable shaft 28 is linked are incorporated inside a cap 8. No description will be given of details at this point.
Firstly, the arc extinguishing chamber 1 and a fixed terminal 2, and the arc extinguishing chamber 1 and a first connection member 4, are joined by brazing, and the cap 8 and a second connection member 5 are joined by welding (laser welding or micro TIG welding). Then, a base plate 7 and the first connection member 4 are joined by seal welding, and the base plate 7 and second connection member 5 are also joined by seal welding. The seal welding is such that joining is carried out by resistance welding (projection welding) or laser welding.
A gas encapsulating type projection welding is such that, as shown in FIG. 6, an upper electrode portion 15 and lower electrode portion 16 inside a gas encapsulation chamber 14 are installed inside the gas encapsulation chamber 14, and it necessary constantly causes a gas 19 to flow in order to maintain a gas atmosphere 18. Because of this, there is a problem in that the gas encapsulation chamber 14 is also unavoidably of a large size. In particular, when inserting a plurality of capsule structure portions 13 in order to carry out seal welding, evacuating and charging of the gas encapsulation chamber 14 are repeated when replacing with the next capsule structure portions 13 on finishing the seal welding. Because of this, there is a problem in that a considerable time is needed for the evacuating and charging of the gas encapsulation chamber. With this kind of step, there is a problem in that the amount of encapsulated gas consumed also increases.
With a gas encapsulating type laser welding, there is a method whereby a plurality of workpieces 24 to and from which hydrogen gas 20 is supplied and evacuated is inserted into a chamber 21 to and from which the hydrogen gas 20 can be supplied and evacuated, and the workpiece 24 is laser welded by a laser beam 25 being caused to fall incident thereon from the exterior of the chamber 21 through a transparent glass window 22, as shown in FIG. 7. With this method, however, a C-shaped supply and evacuation hole 23 is provided in one portion of the workpiece 24, and it is necessary to laser weld the supply and evacuation hole 23. It is necessary to process the C-shaped supply and evacuation hole 23 in advance with high accuracy in one portion of a sealed part, and to set laser irradiation conditions, and weld, in such a way as not to distort the C-shaped supply and evacuation hole 23. Because of this, it cannot be said that the gas encapsulating type of laser welding is a technologically easy manufacturing method. Also, as laser welding is carried out through the transparent glass window 22 of the chamber 21, a large amount of spatter, fumes, and the like, are generated when welding, meaning that there is a problem in that the transparent glass window 22 becomes dirty, and the inside of the chamber 21 becomes dirty easily.
A method whereby a laser welding head is inserted into the chamber 21 and welding carried out has also been disclosed as a method other than laser welding through the transparent glass window 22 of the chamber 21 (for example, refer to PLT 1). With this method, however, there is also a problem in that the size of the chamber increases.
With the heretofore described kinds of gas encapsulating type projection welding method and laser welding method, seal welding is possible provided that the gas encapsulation pressure inside the capsule structure portion is a pressure in the region of atmospheric pressure or slightly higher than atmospheric pressure. However, when the gas encapsulation pressure becomes a gas pressure of a few atmospheres or more higher again, it becomes difficult to carry out seal welding with good mass productivity, while maintaining the gas encapsulation pressure, in the gas encapsulation chamber of the heretofore described kind of gas encapsulating type projection welding method and the chamber of the laser welding method.
Meanwhile, as a method other than the heretofore described welding methods, there is the method shown in FIG. 8. That is, the base plate 7 and pipe 3 are joined in advance by brazing or soldering. Subsequently, the base plate 7 and first connection member 4, and the base plate 7 and second connection member 5, are seal welded by laser welding or projection welding. It should be noted that it is not necessary at this stage to weld while encapsulating gas. Then, in the final stage, gas is encapsulated via the pipe 3, and the pipe 3 is hermetically sealed by being crushed and pressure welded by a pressure tool under a predetermined gas pressure, or hermetically sealed with a handheld ultrasonic welder or the like.
With this kind of method, enclosure and encapsulation are possible with a gas pressure when encapsulating gas of atmospheric pressure or a pressure higher than atmospheric pressure. In this case, however, it is necessary for the pipe 3 to be joined in advance to the base plate 7, and as a method of doing this, a plating processing and hole processing with respect to the base plate 7, and a brazing or soldering of the base plate 7 and pipe 3, are necessary. In particular, as brazing or soldering is a separate step requiring air tightness, unnecessary time is taken. Furthermore, in the case of soldering, the heating temperature is low, meaning that no thermal deformation of the base plate 7 is caused, but there is depreciation in long-term reliability in terms of the strength of the soldered portion. Meanwhile, with brazing, as the brazing temperature becomes high, thermal deformation of the base plate 7 is caused.
Herein, as kinds of gas used in encapsulation, there are hydrogen gas, nitrogen gas, a mixed gas of hydrogen and nitrogen, air, or the like.